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Schizophrenia is a psychological illness that includes positive (e.g., delusions and hallucinations) and negative (e.g., apathy and social withdrawal) signs and symptoms, as well as cognitive impairment (e.g., disorganized thinking).¹

Roughly 1 in 300 people (3%) worldwide are diagnosed with schizophrenia² and, while causes for schizophrenia are unclear, a genetic predisposition,¹ coupled with environmental factors (e.g., adverse experiences during childhood; infection)³, likely contribute to its development.¹

While schizophrenia is not as prevalent as other psychological disorders (e.g., anxiety), the detrimental impact it can have on a person's life is substantial (e.g., family; social; workplace).⁴ And, schizophrenia can co-occur with additional disorders (e.g., panic disorder; posttraumatic stress disorder; obsessive-compulsive disorder; depression; substance abuse; eating disorders)^5;6, putting an even greater strain on quality of life for these individuals.

Eating Disorders and Schizophrenia

 

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Most people with schizophrenia do not meet the full clinical criteria for an eating disorder diagnosis.⁷ Nonetheless, across different research studies, roughly 0.081% to 4% of men and women diagnosed with schizophrenia report anorexia nervosa (AN) signs/symptoms, 0.73% to 3.7% report bulimia nervosa (BN) signs/symptoms, 5.9% to 12.1% report binge eating disorder (BED) signs/symptoms, 8% report night eating syndrome (NES) signs/symptoms, and 30% report nonspecific disordered eating signs/symptoms.⁷

Schizophrenia is more common in men than in women and, unsurprisingly, men are more likely to have simultaneous signs/symptoms of both an eating disorder and schizophrenia compared with women.⁷ For example, on average, men are 3.6 times more likely to have cooccurring signs/symptoms of AN and schizophrenia compared with women.⁷

While extreme psychosis in eating disorders is uncommon, psychosis symptoms frequently occur in association with eating disorder signs/symptoms.⁸ For example, a recent research study found that university students who report lifetime psychosis symptoms, as well as psychosis symptoms within the past 12 months, are more likely to screen positive for an eating disorder compared with students without previous experiences with psychosis.⁹

Explanations for Relationships Between Eating Disorders and Schizophrenia

The coexistence of schizophrenia and eating disorders could be unrelated, as the two disorders might develop independently.⁶ From this perspective, people with schizophrenia have a similar likelihood of developing an eating disorder compared with the general population.

There is evidence, however, that one of these disorders might contribute to the development of the other.⁶ Which disorder is typically observed first, though, is unclear and likely varies across individuals.⁶ For example, in several case reports of men with an eating disorder, the eating disorder preceded patients' schizophrenia diagnosis.¹⁰ In other cases, though, schizophrenia preceded eating disorder signs/symptoms.¹⁰

One explanation for why schizophrenia could contribute to the development of an eating disorder is the prodromal phase of schizophrenia, which occurs before the presence of psychosis in schizophrenia. During the prodromal phase of schizophrenia, people experience anxiety and depression,¹¹ which can contribute to eating disorder development.¹² In fact, Malaspina et al (2019) argue that eating disorder signs/symptoms could indicate the beginning stages of schizophrenia development.¹³ In these cases, disordered eating might reduce over the course of schizophrenia treatment.

 

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It's also possible that psychosis in schizophrenia contributes to the development of restrictive eating, as schizophrenia-related delusions might include paranoia over contaminated or poisoned food.⁶ Psychosis in schizophrenia could also contribute to body self distortions (i.e., difficulties perceiving and interpreting body experiences, like hunger).¹⁴ Difficulties interpreting hunger and fullness cues in schizophrenia could contribute to the development of an eating disorder.

An eating disorder might also contribute to schizophrenia-like symptoms. For example, psychosis could be the result of starvation or electrolyte and metabolic imbalances in people with clinical AN—in these cases, psychosis symptoms might disappear following AN remission.⁶ Restrictive eating might also be a way for people with AN and/or schizophrenia to gain a perceived sense of control over their lives, which is often lacking in people with either of these illnesses.⁶

People with schizophrenia and/or eating disorders also share common genetic variants that increase vulnerability for developing both disorders, with environmental factors contributing to the onset of either illness.^6;15;16 For example, research shows that dopamine genes are dysregulated in people diagnosed with schizophrenia and/or an eating disorder and those who have a family history of either of these disorders.^17;18

The Role of Antipsychotics in Eating Disorder Symptoms in People With Schizophrenia

 

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Atypical levels of certain brain chemicals (i.e., dopamine; serotonin) are one explanation for psychosis symptoms in schizophrenia.¹⁹ The most effective treatment for schizophrenia, therefore, is second-generation antipsychotics (SGAs).^20;21 SGAs are medications that lower dopamine and serotonin levels in the brain. By lowering these brain chemicals, antipsychotics help prevent relapse and rehospitalization for people with schizophrenia.

While SGAs are essential for schizophrenia treatment, these drugs have side effects that could contribute to the development of an eating disorder. For example, side effects of some SGAs are compulsive eating, food cravings, weight gain, and/or body image distortions.^22;23;24 In this way, the use of SAGs in schizophrenia treatment could contribute to the development of BN or BED.^25;26

The brain mechanics of how SGAs influence eating behavior and body metabolism are not entirely understood. We do know that, once in the body, SGAs attach to multiple types of dopamine and serotonin receptors in the brain, which reduces the amount of these chemicals in the brain.²⁷ These chemical changes can have a profound impact on eating behavior. For example, rodent research has shown that SGAs bind to serotonin 2C receptors—the effects of these interactions reduce serotonin in the brain, which increases food intake and contributes to weight gain in rodents.²⁸ These effects make sense given that serotonin reduces appetite and, therefore, decreases in serotonin could increase appetite. The effects of SGAs on food intake are complex, though, and likely involve multiple brain receptors that vary across different SGA types (e.g., clozapine; risperidone).²⁹

Conclusions

While relationships between schizophrenia and eating disorders are unclear, evidence shows that signs and symptoms of each disorder can overlap. Health professionals, therefore, need to consider the best ways to manage co-occurring signs and symptoms of both disorders—these approaches will vary from person to person, with the common goal of improving patient quality of life.

Acknowledging the potential side effects of SGAs in schizophrenia, such as increased appetite and weight gain, are also important for patient well-being. A potential preventative measure for eating disorder development in people with schizophrenia is to provide these individuals with a therapist and/or nutritionist as part of their treatment plan. It might also be necessary to adjust patient dosages of SGAs to reduce side effects that could contribute to eating disorder development.